Traditional manufacturing method of thermal absorbers of solar collectors starts with a roll-to-roll coating process, where flexible and thin substrate material such as copper or aluminium foil is transported continuously through vacuum deposition chambers, wherein it is coated in order to provide selective solar radiation absorbing layers on the substrate material.
After the roll-to-roll coating process, the coated aluminium or copper foil, which delivery form is a coil, is processed for obtaining a thermal absorber having a certain shape and size by opening the coil in order to get a suitable section for removing pieces from the coil, cutting the coated foil to desired foil pieces, and attaching those foil pieces together or with other parts of the thermal absorber such as a cooling fluid tubing. Alternatively, the coil is delivered to a subscriber who processes the coated aluminium or copper foil according to his own needs.
Even though the roll-to-roll process is quite fast, the whole manufacturing process from an uncoated foil to a coated thermal absorber is slow and complex because of several working stages and numerous transfers of uncoated or coated coils from place to another. Furthermore, the attaching process of the metallic foil to the water tubing, e.g. by flame brazing, is expensive, requires sophisticated technology, and connection areas of the thermal absorbers manufactured by such traditional method are prone to failure due to corrosion.